1. Technical Field
The present invention relates to a method for preventing longitudinal transport of fluids--such as water and/or gas through a joint between at least two insulated cable conductors,--including provision of a jointing ferrule for insertion of the conductor ends into the ferrule and making required electrical contacts,--and providing a molded sheath of insulation material over the joint in sealed contact with the conductor insulation.
The invention relates in particular to offshore and subsea cables and the technical problem is to prevent transport of gas and water along the conductors of offshore signal cables when there is a substantial pressure difference between the two ends of the cable. Such pressure difference may occur when one end of a subsea cable has to be lifted to the surface for installation or otherwise. When the sea depth is several hundred meters fluids within the subsea part of a cable will tend to be pressed along the cable core underneath the conductor insulation up to the surface end of the cable. The pressure difference may be more than 10 bars and appearance of such fluids at the top end of the cable is unacceptable.
2. Description of the Prior Art
In U.S. Pat. No. 5,234,515, there is described a method for connecting two electrical conductors. The interconnection between the two insulation sheathed conductors in subsea environments is done using a subsea connector including a metal conductor splice pin arrangement and a splice insulation sleeve. A metal tube is placed over the splice insulation sleeve. The conductor insulation sheaths are molded to respective opposite sides of the metal tube. This solution is too complicated for interconnecting two conductors covered with the insulation material such as PE, and the suggested pretreatment of the metal tube is not capable of preventing transport of pressurized gas/water from one side of the interconnection to the other.
EP 0 639 869 relates to a sealed corrosion-proof crimped terminal or splice aiming at substantially reducing occational cracking of the terminal during the crimping process. There is described use of a splice pin arrangement similar to that mentioned in the above mentioned US patent. The splice pin has an internal wall to provide a water-tight gas-proof barrier between the two conductors. The crimped terminal described may be encapsulated in a protective heat-shrinking tubing or the like,--but it is not likely that any such tubings will prevent penetration of fluids--such as water or gas--under pressure between the tubing and the splice pin from one side of the terminal to the other.
EP 0 341 621 relates to electrical power cables having ethylene polymer insulation with improved endurance against formation of water trees. In connection with this task there is mentioned use of well known components like ethylene-alkylacrylat copolymers and ethylene-alkylacrylat-acrylacid-terpolymer. The problem of formation of water trees in power cable insulation sheaths is, however, quite a different technical field than that of the present invention.